Ah, I looked again now that you mention it. The Chaos codex specifically allows:

"Models in Terminator armor are capable of moving and firing with heavy weapons and may assault after firing rapid fire and heavy weapons."

This is slightly different than the Codex: Space Marine version which gives them the "Relentless" special rule.

According to the main rulebook:

"Relentless models can shoot with rapid fire and heavy weapons counting as stationary, even if they moved in the previous movement phase, and are also allowed to assault in the same turn they fire them."

The Point: Chaos Terminators don't count as stationary for rapid fire weapons, so may only fire them 12" if they move.